1. Field of the Invention
The present invention relates to an improved bicycle brake mechanism and an adapter for use on existing bicycle brakes, particularly those brakes provided as standard equipment on BMX and mountain bikes.
2. Description of the Prior Art
In conventional BMX and mountain bikes, both the front and rear bicycle wheel forks are formed with arms of tubular steel. Caliper brakes are mounted upon both arms of at least the rear bicycle wheel fork. The standard bicycle brake mounting apparatus for both BMX and mountain bikes is comprised of a brake mounting base on each arm. The brake mounting base is formed as a short, steel pedestal having a generally circular cross section secured to each fork arm and projecting in a direction parallel to the plane of the bicycle wheel located between the fork arms. The bicycle mounting bases are welded to the steel fork arms.
Each of the brake mounting bases is provided with a brake axle that projects outwardly in the form of a brake arm mounting post, also in a direction parallel to the plane of the bicycle wheel located between the fork arms. The brake axles have an outside diameter slightly smaller than that of the brake mounting bases from which they project. The brake lever arms that carry the brake pads are mounted for rotation on the brake axles. The brake lever arms each have a mounting end journaled on the brake axle and carry a brake pad at some distance from the axis of rotation of the brake lever arm about the brake axle. When tension is exerted on the brake cable, the distal ends of the brake lever arms are forced inwardly toward each other, thereby forcing the brake pads toward opposing sides of the wheel rim and bringing them into contact with the wheel rim. Friction between the brake pads and the wheel rim slows or stops the rotation of the bicycle wheel.
In conventional BMX and mountain bike construction the outer diameter of the brake axle has been standardized at 0.314 inches (about 8 millimeters). The distance of the brake pad from the axis of rotation of the brake lever arm is adjustable, but is typically in the range of between about five-eighths of an inch (about 15.9 millimeters) to about one and seven-eighths inches (about 47.6 millimeters).
Extremely large forces are developed in the application of bicycle brakes to a bicycle wheel. These large forces produce not only frictional forces that retard rotation of the bicycle wheels, but also torsional moments that act in planes containing the axes of rotation of the brake lever arms. As a consequence, a considerable moment of force is applied to the brake axle tending to deflect it out of proper alignment perpendicular to the plane of rotation of the bicycle wheel. This is visually observable and also noticeable in the sponginess or lack of responsiveness of the brake system. Sometimes the deflection is inelastic to some extent. Indeed, the problem of bent brake axles is so widespread that brake axles are manufactured as disposable components of a brake system. While bicycle brake axles could be manufactured as permanent stub axles welded to and projecting from their respective brake mounting bases, on BMX and mountain bikes they are instead often constructed as removable and replaceable components.
Specifically, in a standard brake mechanism for a BMX or mountain bike, an internally tapped axial bore is defined in each brake mounting base. The brake axle is then formed as a short, detachable post or peg having a cylindrical outer brake arm receiving surface at its distal end and male threads at its proximal end. The brake axle post is provided with a raised, integrally formed, annuler, radially outwardly projecting torque ring at the transition between its distal and proximal ends. This torque ring is typically provided with a pair of diametrically opposed wrench flats that allow the brake axle to be screwed firmly into and removed from the internally tapped bore of a brake mounting base. Alternatively, the annular torque ring may be machined to have the outer surface configuration of a hex nut. In either case a detachable brake axle of this type is known in the trade as a brake boss.
Even though conventional brake bosses are removable and replaceable, they remain susceptible to torsional bending. As a consequence, after installation a conventional brake boss is typically in use only a relatively short time before it bends in a plane passing through its axis. This leads to an imprecise application of the brakes and thus a loss of braking control by the rider.
Various attempts have been made to remedy the problem of lack of rigidity and/or bent brake bosses. However, none of these attempts have remedied the underlying design defect that results in bending of the brake boss along its length.